package cn.thorntail.frpc.core.utils;

/**
 * @see cn.thorntail.core.utils.SHex
 */
public class SHex {

  private static final char[] DIGITS_LOWER = {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f'};
  private static final char[] DIGITS_UPPER = {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F'};

  /**
   * 
   */
  public static byte[] decodeHex(final char[] data) {

    final int len = data.length;

    if ((len & 0x01) != 0) {
      throw new IllegalArgumentException("Odd number of characters.");
    }

    final byte[] out = new byte[len >> 1];

    // two characters form the hex value.
    for (int i = 0, j = 0; j < len; i++) {
      int f = toDigit(data[j], j) << 4;
      j++;
      f = f | toDigit(data[j], j);
      j++;
      out[i] = (byte) (f & 0xFF);
    }

    return out;
  }

  /**
   */
  public static char[] encodeHex(final byte[] data) {
    return encodeHex(data, true);
  }

  /**
   */
  public static char[] encodeHex(final byte[] data, final boolean toLowerCase) {
    return encodeHex(data, toLowerCase ? DIGITS_LOWER : DIGITS_UPPER);
  }

  /**
   */
  protected static char[] encodeHex(final byte[] data, final char[] toDigits) {
    final int l = data.length;
    final char[] out = new char[l << 1];
    // two characters form the hex value.
    for (int i = 0, j = 0; i < l; i++) {
      out[j++] = toDigits[(0xF0 & data[i]) >>> 4];
      out[j++] = toDigits[0x0F & data[i]];
    }
    return out;
  }

  /**
   */
  public static String encodeHexString(final byte[] data) {
    return new String(encodeHex(data));
  }

  /**
   */
  protected static int toDigit(final char ch, final int index) {
    final int digit = Character.digit(ch, 16);
    if (digit == -1) {
      throw new IllegalArgumentException("Illegal hexadecimal character " + ch + " at index " + index);
    }
    return digit;
  }

}
